<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
  a();

  // 函数声明，自动提升
    function a() {
      console.log('调用')
    }

    b();

    // 函数表达式，不会提升，必须先声明后调用
    var b = function () {
      console.log('又调用')
    }
</script>
</body>
</html>